Maximising the utility of bioelectrical impedance analysis for measuring fish condition requires identifying and controlling for sources of error

Abstract Body condition indices are commonly used to represent the physiological status of fishes. Bioelectrical impedance analysis (BIA) has emerged as a rapid, nonlethal and cost-effective method for measuring fish condition and predicting proximate composition components, such as per cent fat. Measuring the condition of fish obtained from varied sources requires consideration of potential sources of error to ensure robust and comparable data are obtained. This is important when opportunistically applying BIA to assess fish condition for species that are logistically difficult to sample (e.g., large-bodied marine fishes), when different sampling methods are used, or where fish handling effects may confound condition comparisons. We experimentally tested the effects of five factors related to fish handling on an instantaneous body condition index (phase angle) measured using BIA. Using the coastal-pelagic yellowtail kingfish (Seriola lalandi) as a model species, we identified significant effects for four out of five factors tested: time since death, temperature of the tissue, removal of the gills and gastrointestinal tract, and the anatomic location for measurements. We propose protocol considerations when using BIA to opportunistically measure condition in fish obtained from varied sources. These sampling protocols for the robust application of BIA can maximise the utility of this approach for opportunistically measuring body condition in fish.